A climbing plant climbs, doesn’t it? So all you have to do is to plant it near some sort of support (trellis, fence, obelisk, pergola, etc.) and away it goes. Except it isn’t always true!
Some so-called “climbers” are actually scramblers (the botanical term is scandent), that is to say, they don’t really climb, they lean. In the wild, they send off long stems in all directions until they find a support they can lean against (a tree, shrub, etc.), then, as they grow, they mingle with branches of their host and therefore manage to climb. In the garden, these plants will rarely climb on their own: you have to direct them to the desired support and tie them to it.
You can use strips of cloth or old pantyhose, foam-covered garden ties, tomato clips, etc. to attach them, but if you use garden twine, wire or plain twist ties, make sure you tie them loosely, as otherwise they will dig into the stem as it expands and eventually “strangle” it (cut off the circulation of its sap).
Climbing roses are the best known scramblers… but indeterminate tomatoes and blackberries also fall into this category. Other plants that scramble rather than truly climb include some honeysuckles (Lonicera x italica ‘Harlequin’ notably), bougainvilleas (Bougainvillea spp.) and plumbago (Plumbago auriculata) . All these plants will crawl rather than climb if you don’t attach them to their support.